The present invention relates to a gear arrangement, for instance for use in a rotary position transducer.
It is known to measure the rotary position of a shaft by using a spur gear arrangement as shown in FIG. 1 of the accompanying drawings. The gear shafts 1 and 2 are held within a housing (not shown) so as to hold the gears 3 and 4 in engagement. The shaft 1 is the shaft whose rotary position is to be determined and the shaft 2 is coupled to or forms part of a potentiometer. The housing and the gears are made of different materials. For example, the gears may be steel so that the gears are strong, but the housing may be of aluminium or an alloy so as to reduce the overall weight of the arrangement. Weight reduction may be especially important in an aeronautical application.
However, using different materials for the gears and the housing gives rise to the possibility of differential thermal expansion between the material of the gears and the material of the housing causing the meshing of the gears to be affected by temperature. Thus, changes in temperature change the distance by which the gear teeth interlock. Such changes in distance introduce backlash between the gears and produce errors in the measurement of the position of the shaft.
It is further known to provide an intermediate gear in the form of an elongate rack 5 biased by springs 6 into engagement with the gears 3 and 4, as shown in FIG. 2. However, if the housing and the rack are formed from different materials temperature changes can introduce spurious measurements since the relative expansion of the rack and housing can cause one of the gears to rotate when the other gear remains stationary.